Method of making a coated embossed steel sheet



Sept? 9, 1958 R. KAPLAN ET AL METHOD OF MAKING A COATED EMBOSSED STEELSHEET Filed Aug. 19, 1955 RoaER-r KAPLAN EDWARD N. SIENKO United StatesPatent METHOD OF MAKING A COATED EMBOSSED STEEL SHEET Application August19, 1955, Serial No. 529,537

1 Claim. (Cl. 113-120) This invention relates to the treatment of metalsheets and products obtained thereby, and more particularly,

to the treatment of coated metal sheets and products obtained therebywhich may be used for decorative or structural purposes.

The instant invention is particularly concerned with the handling ofsheets of the so-called rust resistant metals (i. e. copper, aluminum,stainless steel, etc.) and carbon steel sheets, although the instantinvention may be used with any type of metal sheet, particularly anytype of metal sheet that possesses cold formability at least as good asthe carbon steel sheets here employed. The rust resistant metals havebeen used in sheet form for decorative purposes and/or structuralpurposes for a number of years. The rust resistant sheets such asaluminum and stainless steel sheets have also been embossed in smallstrips to provide ornamental sheets. sheets have been coated, after theyare embossed, with various coating materials and, although the coatingmaterials appear to be rather well anchored because of the irregularembossed surfaces of these metals problems are often presented inconnection with completeness of the coating or continuity of the coatingbecause of the many fine grooves or cuts in the embossed metal.Adherence of the coatings is sometimes impaired also because of bendingof the embossed materials.

To the best of our knowledge others in the industry have not heretoforeembossed carbon steel sheet; but the problems of applying a coating toembossed carbon steel sheet also include the problem of applying acomplete or continuous coating to cover the steel surface at all points.This is particularly important with respect to carbon steel, becausecarbon steel is not a rust resistant metal and a coating applied theretoshould provide protection against corrosion as well as the desiredornamental efi'ect.

As is well known, there are a number of other problems involved in thehandling of sheet steel, usually in the form of hot rolled sheets ofcarbon steel, i. e., steel wherein the principal alloying element iscarbon or steel of the SAE 1000 series. One of the properties ofparticular importance in SAE 1000 series steel is cold formability. Coldforming or cold working of steel is contrasted to hot working in themechanical treatment of steel in that such working is carried out belowthe critical range. The cold working of steel involves a number ofoperations including cold forming, which may involve merely bending orstamping, or it may involve the relatively more difiicult operation ofdrawing.

In drawing a generally flat sheet of metal is subjected to bendingcombined with a shearing force, but the metal having good drawingquality yields to the shearing tions.

These force to the extent that it is deformed in drawing rathersubstantially less brittle. In general;drawtsgarivaivs the formation ofa dish-shaped article from a generally flat metal sheet and thisoperation is contrasted to mere stamping or bending in that the metalhaving deep drawing quality is capable of being drawn perhaps fourinches using a piece one square foot in area. Extra deep drawing mayinvolve the formation of as much as an eight inch depression in a onesquare foot sheet of metal.

It is also well known that the concentration of forces is so great inthe cold drawing operation that metallurgical changes are effected incertain steels, usually to the extent that'brittleness may be impartedto higher carbon steels. On the other hand, higher carbon steels such asSAE 1020 have increased rigidity or strength so as to resist colddrawing and make the operation much more difficult from the point ofview of forces applied as well as wear and tear on the dies. In general,it has been the practice in industry for some time to use carbon steelsin the series SAE 1006 to SAE 1015 (i. e., having about 0.05-0.15% C andabout 0.300.60% Mn) for drawing automobile body and fender stock, lamps,oil pans, and a number of other deep drawing opera- Steel of this type,usually referred to as mild steel, possesses very good ductility or theability to withstand cold deformation, but it possesses such ductilityat a sacrifice in strength or rigidity.

Coatings applied to such carbon steels of the type which adhere ratherwell to the carbon steel tend to separate therefrom upon bending orsubsequent treatment of the carbon steel, and particularly upon drawingor actual cold forming of the carbon steel. The same is true of coatingsapplied to the rust resistant metal sheets which are subsequently coldformed or drawn. There are a vast number of coatings which may beapplied to such metal sheets, but in general the coatings with which weare here concerned are coatings which are formed of materials having acertain amount of deformability as contrasted to the very great rigidityof a porcelain enameling coating, for example. Such coatings aregenerally recognized in the art as flexible or deformable coatings, suchas electroplated metal, resin coatings eitheras natural resins in paintsor varnishes or as synthetic resins alone or in paints or varnishes, andthe like. Such coatings are deformable at least to the extent that theyare no more brittle than the carbon steel sheets here employed (or theyare no more brittle in the form of thin coating films than the carbon.steel sheet here employed). In other words, theese materials arecapable of deformation at least to the same extent (and usually muchmore easily) as the metal sheet itself. Notwithstanding this fact itappears that such coatings tend to separate from the metal backing whenthe same is bent or otherwise formed into a desired shape. I

The instant invention affords a solution to many problems confrontingtheworkers in this art. A key to the instant invention resides in theconcept of applying such deformable flexible coatings to the metalsheeting as an initial treatment, followed by embossing of the coatedsheet, before drawing and/ or other secondary operations The embossingof the coated sheet apparently brings about a number of unique andimportant advantages,

some of the more striking including ease of drawing, and

substantially better adherence ofthe coating itself insubsequentoperation such as drawing.

An important object of the instant invention is to provide an improvedmethod of handling metal sheets, and particularly in the application ofcoatingsithereto, and further to provide improved coated metal sheetsand articles formed ther'efrom. It is a further object oflthe instantinvention to provide an improved process which comprises applying a thincoherent filmusf deformable coating" material to "a metal sheet,followed by embossing the coated sheet; and to provide an improvedproduct resulting therefrom.

Other objects, features and advantages of the instant invention willbecome apparent to those skilled in the art from the following detaileddisclosure thereof and the drawings attached hereto and made a parthereof.

On the drawings:

Figure 1 is a detail view in section of a metal sheet having a coatingapplied to one side thereof;

Figure 2 is a top plan view of one modification of an embossed coatedmetal sheet embodying the instant invention;

Figure 3 is a sectional elevational view of an embossed coated sheet ofthe instant invention (such as that shown in Figure 2) which has beendrawn to form a generally dish-shaped panel, for example, for arefrigerator door or the like; and

Figure 4 is an enlarged sectional detail view taken substantially alongthe line IV-IV of Figure 2.

As shown onthe drawings:

In Figure l, the reference numeral indicates generally a metal sheet 10ahaving a coating 11 on one side thereof. The metal sheet 10a is a fiatsheet of substantially uniform thickness and the coating 11 is a flatcoating of substantially uniform thickness. An initial step in themethod of the instant invention involves applying the coating 11 to thefiat metal sheet 10a by any of a number of methods which will bedescribed hereinafter. Next, the sheet 10 is embossed to provide a sheet10' of Figures 2 and 4.

Referring to Figures 2 and 4, it will be noted that the sheet 10' has amultitude of alternating bosses or raised portions 11a, 11b, 116, etc.surrounded by valleys or depressions 12a, 12b, 12c, etc. on the coatedface thereof. The coating 11' has conforming peaks 13a, 1311, etc. andvalleys or depressions 14a, 14b, etc. Because of the greater ease ofdeformability of the coating 11, the thickness of the coating 11' maynot necessarily remain uniform throughout, but the embossing processserves to effectively trap the coating 11 so that an appreciablethickness thereof remains over the entire surface. There are alsodepressions 15a, 15b, etc. and bosses 16a, 16b, on the rear or uncoatedside of the metal sheet 10a corresponding to opposed bosses ordepressions as the case may be. For example, the boss 11a on the coatedside has a corresponding depression 15a on the uncoated side and thedepression 12b on the coated side has a corresponding boss 16a on theuncoated side. This is the general outline of the cross-sectional shapeof the embossed sheet 10', although the positioning of the bosses andrecesses on the opposite faces thereof need not be positioned with suchprecise regularity or uniformity, so long as the recesses on one sideare opposed generally to the bosses on the opposite side. In fact, it isgenerally preferable to present a surface in the form of the coating 11'as shown in Figure 2 wherein the positioning of the bosses appears to bea random positioning such as in simulated stucco, rather than aperfectly uniform positioning. Such an arrangement is generally moreornamental and attractive to the observer. Actual designs presentinggreater uniformity or symmetry in the positioning of the bosses may beused, however, to substantially the same advantage in the practice ofthe instant invention.

In carrying out the coating step in the practice of the invention, itwill be appreciated that any of a number of well known coating methodsmay be employed and any of a number of well known coating materials maybe employed. The materials which may be employed in coatings includeresinous or plastic materials such as natural resins in rosin-base orcellulosic derivative-base paints, varnishes or lacquers, with orwithout pigments, and synthetic resin-base paints, varnishes orlacquers, with or without pigmentation. Also, the coating material maybe a metal applied by electro-plating, for ex ample. In general, thecoatings may be applied in thicknesses ranging from a practical minimumof about 0.001 inch in order to cover the surface of the material with acoherent film to a practical maximum of about 0.010 inch, above whichresults in unnecessary loss of the coating material during the embossingstep. The coating material is a deformable material having a degree oftoughness suflicient to permit deformation of the extent here obtained.The extent of the deformation here obtained will be described inconnection with the embcssing step proper; and the material employed inthe instant coating composition should be capable of deformation to thisextent without breaking (i. e., the material should not be so brittlethat it breaks when undergoing such deformation). The material is thusnot more brittle than the carbon steel sheet (which is probably the mostbrittle form of metal base material used in the practice of theinvention).

In carrying out the embossing step, it has already been mentioned thatcarbon steel sheet may be used as the base material. Such sheet may haveabout 0.05- 0.30% C, and preferably has only about 0.30-0.90% Mn. Thisinvolves the steels within the range SAE 1006 to SAE 1030, except forSAE 1019, 1022, 1024, and 1027 which have higher Mn contents (of as muchas 1.65% Mn). Preferably, the Mn content is 0.25- 0.60%, using Ccontents as high as 0.30%; and in many instances the greatest advantagesof the instant invention are obtained using steels within the range SAE1006 to SAE 1015 (ODS-0.15% C and 0.25-0.60% Mn).

The advantages obtained using carbon steel sheet are quite unique inthat a protective coating for carbon steel sheet is required in order toprevent excessive corrosion, as by rusting. There are a number ofstructural advantages obtained from embossing a plain carbon steelsheet; but the embossed sheet must then be painted or coated in mostinstances to prevent corrosion thereof. Although coating films will inmany instances adhere very well to an embossed carbon steel sheet, theapplication of such coatings is often complicated by the difficulties inapplying coatings so as to completely cover the metal in the variouscrevices on the surface thereof without employing so much coatingmaterial that the openings or crevices in the surface are substantiallyfilled by the coating material. This tends to alter the appearance andthe con tour of the surface. Instead, in the practice of the instantinvention the coating is applied in a uniform thin film before theembossing process and the coating remains on the surface after theembossing process in a correspondingly thin film which is forced intoeach of the various crevices or openings and which completely covers themetal therein. Also, substantially better adherence between the coatingand the metal is obtained if the embossing step is carried outsubsequently, in accordance with the teachings of the instant invention.This advantage is also obtained in the use of the so-called rustresistant metals; and, of course, protective coatings are often appliedto the so-called rust resistant metals also because of peculiarcorrosion problems which may arise.

The thickness of the sheets of metal backing material employed in thepractice of the instant invention may range from a maximum of about 0.1inch to a practical minimum of about 0.01 inch. Preferably 18 gauge(0.050 inch thickness) or less is used.

In general, the embossing operation is a cold working or cold formingoperation. The coated sheet is passed between matched hard steelembossing rolls, at cold working temperatures preferably, and theembossing rolls are provided with a multitude of small bosses matinglyaligned on the two rolls so as to avoid having the bosses on one rolldirectly opposite the bosses on the other roll at the embossing niptherebetween through which the sheet passes. The bosses, in order toobtain the full benefit of the instant invention, have an averageheightor extend an average distance from the'roll periphery of about 0.010 toabout 0.014 inch for embossing stock of 0.035 inch thickness (or forthat matter for embossing stock over the entire operativerangehereinbefor'e set forth, the size of the bosses being optionally alteredto conform somewhatto variations in thickness of the sheet). Expressedin other terms, the bosses are approximately 4 to /2 of the sheetthickness in height and preferably about 20 to 45% of the sheetthickness in height. The distances a, d (Figure 4) betweenthe tops ofthe bosses and the depressions in the sheet are substantially the sameas the proportions just given for the bosses on the embossing rolls,although the distances just mentioned on the sheet may be slightlylessif completely elfective'embossing is not accomplished because of spacingbetween the rolls or reduced pressure at the nip.

p The embossing operation (with the possible exception of'the overallpressures used) is substantially the same for each of the variouscoating materials and each of the various coated base sheetshereinbefore described. The embossingprocess may thus be carried outusing carbon steel sheeting of carbon content'up to as high as perhapsSAE 1052 (about 52% carbon and as high as 1.55%

Mn), but there are practical limitations such as wear and tear on'theembossing rolls or dies which would subtract to an appreciable extentfrom the overall advantages of the instant invention if too hard acarbon steel were used. Also, the relatively poor cold formability ofsuch high qualityif it can be drawn four inches per square foot. Thedrawing operation itself involves applying suitably formed male andfemale dies to the sheet material under pressure (at less than thecritical temperature for cold drawing) in order to effect deformation ofthe sheet to form the dish-shaped article. As mentioned, drawing of thesheet to the ultimate shape need not be accomplished in a single drawingstep but may be accomplished through series of successively deeperdraws, with heat treatment in-between such steps (if a refractorycoating such as an electro-plated metal has been applied).

Referring to Figure 3, it will be seen that an embossed sheet such asthe sheet 10' (Figure 2) may be drawn to C and high Mn steels wouldnecessitate greater embossing operating pressures and greater care incarrying out the operation, the operation in suchcases necessarilyresults in metallurgical changes in these high C-Mn steels which requiresubsequen t heat treatment. In any event, however, the embossedsteelsh'eets of the invention afford unusualadvantages in cold forming.This is also the case in connection with embos sed rust resistant metalsheets. As an example, the embossingstep effects a definite increase inrigidity or strength of approximately 25 to over unembossed stock; butcontrary to expectations this increase in rigidity greatly facilitatesrather than making more difficult cold forming operations. In addition,the coatings further facilitate cold forming operations and permit coldforming operations without effectively losing the coating on the surfaceof the embossed material. Wear and tear on the die is reduced presumablybecause there is less metal-to-metal contact and a better chance forlubrication (rather than increased as might be expected because of thesupposedly roughened metal surface of the embossed workpiece). Thisafi'ords an advantage even in the case of the higher carbon steels, ifcoated with a suitably refractory coating, which may have to be heattreated once or several times during any sort of cold forming operation.

The drawing operation which is employed to particular advantage in theinstant invention is, of course, a standard drawing operation of thetype well known to those skilled in the art. The differences hereinvolved include greater ease of drawing, apparently better lubricationbetween the die and the workpiece, less wear and tear on the die, aretention of the embossed contour of the workpiece during the drawing orforming operation, and a retention of the embossed contour of thecoating on the base metal during the drawing or forming operation. Inother respects, the drawing operation is the same as an ordinarycommercial operation. Drawing itself is a well known art and need not bedescribed herein in detail. For the sake of distinguishing from ordinarybending, stamping or cutting operations drawing could probably best bedefined as involving the application of forces to the workpiece that arecomparable to forces at least suflicient to make a two-inch depressionin a square foot of the workpiece sheet. Expressed in other terms,drawing involves the shaping of a sheet into a dish-shaped article or anarticle having a bowed contour; and the workers in the art generallyconsider a material has good deep drawing form a generally dish-shapedpanel member 17 wherein the central portion 17a is recessed about fourinches, as the dimension r indicates, and a flange-like portion 17b isretained around the periphery. The drawing operation is accomplished inan ordinary drawing press so as to provide a dish-shaped front panelmember 17 for a door, such as an ice box door. In Figure 4, the contourof the coated embossed sheet 10 is shown.

For example, sheets of material are prepared for embossing, according tothe instant invention, by carrying out the following procedures: I

(1) Using-20 gauge SAE 1010-steel sheeting as a cathode, plating iscarried out using a chrome plating bath (having 280 g./l. CrO and 2.8g./l. H SO content) maintained at 130 F.,withcathode current density; of200 a. s. f. (amperes per square foot) and an anode current density ofa. s. f., using ale'ad anode, and plating for 10 minutes.

(2) Using 20 gauge SAE 1015 steel sheeting as a cathode, plating iscarried out in an electrolyte containing zinc (content: 4.5 oz./gal. ofZn, 12.5 oz./gal. of NaCN, 10.5 oz./ gal. of NaOH) maintained at 95 F.with a cathode current density of 20 a. s. f. and a (zinc) anode currentdensity of 10 a. s..f., 'and plating for 10 minutes.

(3) Using about 0.050 in; 18-8 stainless steel sheeting as a cathode,plating is carried out in an electrolyte containing copper (content: 3oz./ gal. of Cu, 4 oz./gal. of Cu(CN) 6 oz./gal. of NaCN) maintained atF. with a cathode current density of 40 a.'s. f. and a (copper) anodecurrent density 'of20 a, s..f.; and plating for 10 minutes.

(4) Using 18 gauge SAE 1010 steel sheeting as a cathode, plating iscarried out in an electrolyte containing cadmium (content: 3 oz./ gal.of Cd, 12 oz./ gal. of NaCN, 3 oz./ gal. of NaOH) maintained at 90 F.using a cathode current density of 20 a. s. f., and a (cadmium) anodecurrent density of 10 a. s. f., and plating for 10 minutes.

The foregoing metal plated sheets are embossed in the mannerhereinbefore described by passing the same through a nip defined bymatched hard steel embossing rolls at cold working temperatures, therolls having bosses thereon of an average height of 0.012 inch; and theresulting embossed sheets have superior cold formability and can bedrawn to form panels such as the panel shown in Figure 3. In theseembossed sheets, it is noted that the metal plating adheres well duringthe embossing operation and during subsequent cold forming operationssuch as the drawing operation.

Substantially the same results are obtained using sheets of otherrust-proof metals such as aluminum and plating with the aforementionedplating baths or plating baths depositing other metal coatings. Also,silver coatings deposited chemically (as in the formation of mirrors)may be applied to the carbon steel sheets or the rust-proof metal sheetsused herein and the resulting coated sheets may be embossed to obtainthe advantages of the instant invention.

Among the non-metallic coatings which may be employed in the practice ofthe instant invention those of the greatest significance are the naturaland/ or synthetic resin coatings. Among this group the so-calledelastomers are preferred. The resin or plastic elastomers are well knownmaterials to those skilled in the art possessing generally elastomericproperties comparable to that of natural rubber. Such elastomers includerubber, chlorinated rubber, rubber-synthetic resin admixtures, syntheticrubbers (i. e. butadiene-styrene, isoprene, chloroprene,butadiene-acrylonitrile copolymers), flexible (or unsaturated) polyesterresins, vinyl chloride polymers, vinyl chloride-vinylidene chloridecopolymers, vinyl chloride-vinyl acetate copolymers, and the like. Theseresin or elastomer coatings may be applied per so as by flame-spraying,which is particularly effective with polyethylene andpolytetrafluoroethylene (which are well known elastomers), or the resinsmay be applied in solution in organic solvents with subsequent bakingoperations to remove the solvent, or the resins may be applied inemulsion form in aqueous media also with subsequent drying to remove thecarrier. Solutions or emulsions of the resins may be applied byspraying, dipping, painting, or the like. Special treatments for themetal surface prior to the application of such resins may also beemployed, such as the bonderizing, or Parkerizing processes. Pigmentsmay be included or omitted as desired, but since decorative effect is animportant feature in many uses of the invention, various coloredpigments are usually included so that an elastomer base paint ispreferred in many instances.

Specific examples of coatings include the following:

Vinyl chloride-vinylidene chloride commercial grade medium copolymer isapplied in a film 0.05 in. thick on 18 gauge SAE 1010 sheeting from amineral spirits solution sprayed on followed by baking at 350 F. to dryand cure the coating.

(6) Paint containing green pigments and vinyl chloride-vinylidenechloride commercial grade medium copolymer is applied in a film 0.05 in.thick on 20 gauge SAE 1010 sheeting, from a commercial aqueous emulsionfollowed by baking at 350 F. to dry and cure the coating.

(7) Polyethylene is flame-sprayed on 0.050 in. thick 18-8 stainlesssteel sheet to provide a continuous film of 0.03 in. average thickness.

(8) Polytetrafluoroethylene is flame-sprayed on 0.050 in. aluminumsheeting to provide a continuous film of 0.03 in. average thickness.

(9) Commercial flexible (unsaturated) polyester resin (i. e. ethyleneglycol-propylene glycol-phthalate) in varnolene solution is painted onto20 gauge SAE 1010 sheeting and cured at 200 F. to obtain a film of 0.05in. average thickness.

Each of the foregoing coated sheets is embossed in the mannerhereinbefore described (i. e., using embossing rolls having bossesthereon of an average height of 0.012 inch) and it is found that theembossed sheets may be bent back and forth without causing the resincoating thereon to crack or separate from the metal. Also, the embossedsheets are cold formed in panels such as the panel shown in Figure 3 bydrawing and it is found that the drawing process is simplified eventhough the embossed panels have greater rigidity, and the coating is notharmfully affected by the drawing process.

It .will be understood that modifications and variations may be efiectedwithout departing from the spirit and scope of the novel concepts of thepresent invention.

We claim as our invention:

A method which comprises applying a thin coherent 0.001 to 0.01 inchthick film of deformable thermoplastic synthetic elastomeric resinouscoating material to 0.01 to 0.1 inch thick carbon steel sheet, pressureembossing the coated sheet by passing the coated sheet through a pressnip defined by embossing rolls having bosses thereon having a height of0.1 to 0.5 times the sheet thickness, and then cold drawing the embossedcoated sheet without eradicating the embossing.

References Cited in the file of this patent UNITED STATES PATENTS1,499,985 Kirsch July 1,1924 1,773,926 Michael Aug. 26, 1930 1,892,754Tarbox Jan. 3, 1933 1,934,256 Bronson Nov. 7, 1933 2,114,150 Rodman Apr.12, 1938 2,120,461 Copeman June 14, 1938 2,122,537 Pfetfer July 5, 19382,166,226 Vehko July 18, 1939 2,387,919 Lose Oct. 30, 1945 2,735,390Engel Feb. 21, 1956 OTHER REFERENCES Pages 102, 103 of ProductEngineering, March 1949.

